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CHAPTER 2
CHROMOSOME,CELL CYCLE, CELL DIVISION, Formation of new DNA…
CHAPTER 2
CHROMOSOME,CELL CYCLE, CELL DIVISION
CHROMOSOMES=
The nucleus contain DNA which are organised into discrete manner called chromosomes
Chromosomes are coiled and condensed chromatin fibre
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Genes
Are specific sequence of nucleotides in a chromosome.
that encode particular protein which express particular feature of the body
CELL CYCLE
Divide,grow,redivide
"Cells perform these tasks in a organised,predictable series of events which is called the cell cycle
Inter-phrase
Is a phrase of cell where the daughter cells have little cytoplasm but a full sized nucleus
First growth phrase
RNA and proteins are synthesized to increase the cytoplasm. They either withdraw from the cell cycle and enter a resting phrase Or move into the next phrase (Synthesis)
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Second Growth Phrase
In this phrase RNA and proteins are necessary for cell division. Now the cell is ready to undergo Cell division
Growth of cells
Brain and nerve cells
Once formed in the embryo they don't divide further. Once dead they cant be replaced
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Specialised Germinal cells in the ovary and testies undergo special type of cell division called Meiosis
Cell division
mitosis
Cell Division in which one parent cell divides into two daughter cells
In mitosis each cell has same normal chromosome number is maintained at each cell division
Karyokinesis
prophase
Is the phrase of mitosis in which two that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses.
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Anaphrase
Chromatids end up moving to opposite poles(Due to Contraction OF spindle fibers)
Furrow of the cytplasm
Telophrase
The two daughter cells reach opposite ends.
The spindle fiber disappears.
Nuclear membrane is Formed.
Nucleoli reappears.
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Formation of new DNA cells
IN a DNA double helix opens at one end making two strands free to which the new strands are attached this process continues in a sequence for the whole length of the DNA
Cytokinesis
Division of cytoplasm
Cleavage furrow deepens totally in animal cells and separates he two daughter cells
Need of new cells
Growth
Cell in organism,including plants and animals divide to form cluster of cells to form tissue and organs
Replacement
In animals almost 2 million cells are destroyed each second these are restored
from new cells in the bone marrow
Repair
The accidental injury needs to be repaired by cell which divide
Reproduction
takes place by these actively dividing cells like in amoeba
